Firefox will cease XP support as of ESR v52 (so that one will run on XP). So v51 will be the last mainline release supporting XP.
https://bugzilla.mozilla.org/show_bug.cgi?id=1303827
Oddly enough, and I only recently learned this, that current x64 versions of Waterfox still support Windows XP x64 Edition.
https://bugzilla.mozilla.org/show_bug.cgi?id=1303827
Oddly enough, and I only recently learned this, that current x64 versions of Waterfox still support Windows XP x64 Edition.